Compositions and Methods of Preventing Erythropoietin Associated Hypertension

ABSTRACT

The inventors have discovered that both soluble erythropoietin-binding protein and antibodies against the erythropoietin-binding protein, when they are administered to a mammal along with erythropoietin (Epo), prevent or reduce the blood pressure increase normally caused by erythropoietin, while not affecting the hematocrit increase that is the purpose of Epo treatment. The invention provides a method of treating anemia in a mammal involving: administering erythropoietin (Epo) to the mammal; and administering to the mammal an agent selected from a soluble Epo-binding protein (Epo-bp), a recognition protein that binds Epo receptor on an extracellular soluble portion of the Epo receptor, and a combination thereof. 
     The invention also provides a method of reducing hypertension in a mammal receiving Epo, and pharmaceutical compositions containing a soluble Epo-bp and/or a recognition protein that binds Epo receptor on an extracellular soluble portion of the Epo receptor.

This nonprovisional patent application claims priority from and is acopending continuation of U.S. application Ser. No. 14/042,702, filedSep. 30, 2013, which was a copending continuation of U.S. applicationSer. No. 13/044,818 filed Mar. 10, 2011, which was a copendingcontinuation of U.S. application Ser. No. 10/848,689, filed May 17,2004, which applications are incorporated herein by reference thereto.

The research and development of the invention described herein did notinvolve any federally sponsored funding.

BACKGROUND OF THE INVENTION

Erythropoietin is sold under the labels PROCRIT (epoetin), EPOGEN(epoetin), and ARANESP (darbepoetin). Erythropoietin is indicated fortreatment of anemia, particularly anemia associated with chronic renalfailure and cancer chemotherapy. Erythropoietin (Epo), an angiogenicfactor, increases hematocrit and hemoglobin concentrations via thestimulation of erythropoiesis, resulting in increased blood viscosity(1-5) and blood pressure (1-14). In clinical studies, approximatelyone-third of hemodialysis patients treated with recombinant human Epohave shown an increase in blood pressure. Epo has been postulated toincrease peripheral vascular resistance and decrease cardiac output dueto increased viscosity (6). Others have suggested additional mechanismsfor Epo-caused hypertension, such as hypervolemia, increased plasmarenin and angiotensin, along with adrenergic over activity, increasedplasma arginine vasopressin, decreased kinins and prostaglandins (15).An excessive, lasting elevation of circadian amplitude, blood pressureover-swinging and an elevation of blood pressure may be based onvasomotor chronome (time structure) alteration. Hormones and otheragents, in part on a genetic basis, may be contributing factors to thecircadian blood pressure variation. Hypertension is one of the mostimportant risk factors in the development of cardiovascularcomplications. Hypertension is affected significantly by circadianrhythms. Hormonal concentration in the body fluctuates during the dayand night with prominent spontaneous circadian (about-24-hour) changesthat affect blood pressure and heart rate. There are also sufficientlyimportant rhythms that can make the difference between the stimulationversus the inhibition of a malignancy. Epo is a 34 kDa glycoproteinhormone that is produced by the interstitial cells in the peritubularcapillary bed of the mammalian kidney and the perivenenous hepatocytesof the liver (3). Epo is secreted in response to hypoxia to coordinateerythropoiesis as a primary inducer and regulator of red-celldifferentiation by suppressing apoptosis and triggering cell divisionand terminal maturation of blood cell progenitors (16). These effectsare mediated through the binding of Epo to specific cell surfacereceptors (17). The primary structure of human Epo has been known sincethe mid-1980s (18,19), but the structural features of the Epo moleculethat confer its biological activity are largely unknown. Human Epocontains two disulfide bonds that link cysteine 29 with cysteine 33, andcysteine 7 with cysteine 161. Both bonds are essential for biologicalactivity (18). Epoetin (recombinant human erythropoietin) was producedfollowing isolation of the human gene and its expression in a Chinesehamster's ovarian cell line (4).

The recombinant Epo is a 165-amino acid mature protein that differs fromthe mature native protein only in lacking the carboxyl terminus arginineof the native protein. Native human Epo is translated as a 193-aminoacid peptide, from which a 27-amino-acid leader sequence is cleaved off(19,20). Recombinant Epo has an apparent molecular weight of about 30.4kDa, appears to be immunologically equivalent to the endogenous hormone,and exhibits full biological activity (19).

Epo-treated humans and animals exhibit increased hematocrit % andincreased hemoglobin via the stimulation of erythropoiesis (2-5). Somestudy results suggest that increased hematocrit levels are correlatedwith an increased blood pressure in humans (20). Other studies involvingthe treatment of anemia with Epo showed increased hematocritconcentrations and resulting elevated blood severe enough to requiretreatment with antihypertensive medication pressure in 20-30% ofpatients (5). Hypertension is the most frequent and most importantcomplication from treatment with erythropoietin. Furthermore, althoughthe goal of Epo treatment is to increase hematocrit and hemoglobin, ithas been found and well understood that the greater the increase ofhematocrit, the greater the risk of mortality and cardiovascular events.This may be due to blood pressure rise, since the extent of bloodpressure rise has been shown to correlate with the extent of hematocritincrease (20). The epoetin label warns that patients with uncontrolledhypertension should not be treated with epoetin. New methods andcompositions to prevent or treat blood pressure rise in patients treatedwith Epo are needed. New methods and compositions to treat anemiawithout causing hypertension are needed.

SUMMARY OF THE INVENTION

The inventors have discovered that a soluble Epo-binding protein, whichis a soluble fragment of the membrane protein Epo receptor, whenadministered to mammals along with Epo, prevents the blood pressureincrease ordinarily caused by Epo, while not affecting the rise inhemoglobin and hematocrit that is the goal of Epo treatment. An antibodyagainst Epo-binding protein was also found to prevent the Epo-causedblood pressure increase while not affecting the Epo-induced hematocritrise. Accordingly, the invention provides a method of treating anemia ina mammal involving: administering erythropoietin (Epo) to the mammal;and administering to the mammal an agent selected from a solubleEpo-binding protein (Epo-bp), a recognition protein that binds Eporeceptor on an extracellular soluble portion of the Epo receptor, and acombination thereof. Another embodiment of the invention provides amethod of reducing hypertension in a mammal receiving Epo involvingadministering to the mammal an agent selected from a soluble Epo-bindingprotein (Epo-bp), a recognition protein that binds Epo receptor on anextracellular soluble portion of the Epo receptor, and a combinationthereof. Another embodiment of the invention provides use of arecognition protein that binds Epo receptor on an extracellular solubleportion of the Epo receptor in medical therapy. Another embodiment ofthe invention provides use of a recognition protein that binds Eporeceptor on an extracellular soluble portion of the Epo receptor toprepare a medicament effective to reduce erythropoietin-inducedhypertension. Another embodiment of the invention provides use of asoluble erythropoietin-binding protein in medical therapy.

Another embodiment of the invention provides use of a solubleerythropoietin-binding protein to prepare a medicament effective toreduce erythropoietin-induced hypertension. Another embodiment of theinvention provides a pharmaceutical composition including:erythropoietin; and an agent selected from a soluble Epo-binding protein(Epo-bp), a recognition protein that binds Epo receptor on anextracellular soluble portion of the Epo receptor, and a combinationthereof. Another embodiment of the invention provides a pharmaceuticalcomposition including: a recognition protein that binds Epo receptor onan extracellular soluble portion of the Epo receptor. Another embodimentof the invention provides a pharmaceutical composition including: asoluble Epo-binding protein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bar graph showing the average circadian blood pressure ofeach of the treatment groups of rats treated with Epo and other agents.Error bars represent standard error, SEM.

FIG. 2 shows the circadian blood pressure measurements for each of thetreatment groups.

FIG. 3 is a representation of the circadian hematocrit variation in thetreatment groups of rats.

FIG. 4 is the outline of photographs of spleens isolated from ratstreated with Epo (panels A, B, and C), or saline (panel D).

FIG. 5 is a bar graph of optical density from immunodetection of Epo,VEpo, Epo-bp, and VEpo-bp in serum and plasma of human volunteers. Errorbars represent standard error, SEM.

DETAILED DESCRIPTION Definitions

“Erythropoietin” as used herein includes erythropoietin isolated fromnatural sources and recombinant or engineered erythropoietin that hasthe biological activity of erythropoietin of stimulating red blood cellproduction. It includes epoetin and darbepoetin. Preferably, theerythropoietin has at least 70%, more preferably at least 90%, aminoacid sequence identity with human erythropoietin, SEQ ID NO:3. Sequenceidentity is calculated using the default BLAST parameters for nucleotidesequence comparison at the PubMed website, www.ncbi.nlm.nih.gov/PubMed/.

As used herein, “a soluble Epo-binding protein” refers to a protein thatis not an antibody, is water-soluble, binds erythropoietin with highaffinity, and when administered with Epo to mammals is effective atreducing an Epo-induced blood pressure rise in the mammals. Preferably,the KD of the protein for binding with erythropoietin is less than 10:M, more preferably less than 1: M, more preferably still less than 100nM, and most preferably less than 20 nM. KD can be determined bycompetition binding assays such as described in Example 6 of U.S. Pat.No. 5,843,726. Preferably, the soluble Epo-binding protein is orincludes sequences from or sequences homologous to the soluble portionof an Epo receptor. The human Epo receptor sequence is SEQ ID NO:1(Winkelmann, J. C., et al., 1990, Blood 76: 24-30). The soluble portionof the human Epo receptor is residues 25-250 of SEQ ID NO:1.

In a particular embodiment, the residues of the Epo-binding proteinresponsible for binding Epo are at least 70% identical, more preferablyat least 80% identical, more preferably at least 90% identical, mostpreferably identical, to the corresponding residues of SEQ ID NO:1.

As used herein, “an extracellular soluble portion of an Epo receptor”refers to the portion of the Epo receptor that is exposed on theextracellular surface of the cell in the aqueous environment.Specifically, it refers to SEQ ID NO:2, which is residues 25-250 of SEQID NO: 1 (the human Epo receptor), or to the homologous soluble residuesof another Epo receptor protein.

As used herein, “a recognition protein that binds Epo receptor on anextracellular soluble portion of the Epo receptor” refers to a proteinthat binds the extracellular soluble portion of Epo receptor and that,when administered to mammals along with Epo, reduces an Epo-inducedblood pressure rise in the mammals. The recognition protein can be acomplete antibody raised against an Epo receptor or against anEpo-binding protein, where the antibody binds the soluble portion of Eporeceptor, or a binding fragment of such a complete antibody. Therecognition protein can also be a non-antibody protein or peptide (e.g.,a protein or peptide selected by phage display binding) that binds tothe extracellular soluble portion of the human Epo receptor or ofanother mammalian Epo receptor with a binding affinity of at least 105liters per mole, more preferably 106, more preferably at least 107, mostpreferably at least 108 liters per mole.

As used herein, the term “antibody” includes complete antibodies andantigen-binding fragments of complete antibodies, e.g., Fab or F(ab′)2antibodies. The term “antibody” also includes both monoclonal andpolyclonal antibodies (e.g., antiserum).

The term “reducing hypertension” by administering an agent includespreventing or reducing an increase in blood pressure that otherwiseoccurs in a significant fraction of a population when the agent is notadministered.

Description:

The methods of the invention involve administering to the mammal anagent selected from a soluble Epo-binding protein (Epo-bp), arecognition protein that binds Epo receptor on an extracellular solubleportion of the Epo receptor, and a combination thereof. In someembodiments of the invention, the agent is a soluble Epo-bp. In someembodiments, the soluble Epo-bp contains a fragment of a soluble portionof a mammalian Epo receptor.

In particular embodiments the soluble Epo-bp comprises a fragment of atleast 30 residues of SEQ ID NO:2 (residues 25-250 of human Epo receptor,SEQ ID NO: 1). SEQ ID NO:2 is the extracellular soluble portion of thehuman Epo receptor. In other particular embodiments, the soluble Epo-bpcomprises a fragment of at least 15, at least 50, at least 100, at least150, or at least 200 residues of SEQ ID NO:2.

In particular embodiments, the soluble Epo-bp includes or is SEQ IDNO:2. The soluble Epo-bp that is SEQ ID NO:2 can be expressed asdescribed in U.S. Pat. No. 5,843,726. In general terms, SEQ ID NO:2 isexpressed as a fusion protein with a glutathione S-transferase (GST)N-terminal leader sequence. SEQ ID NO:2 is separated from the GST leadersequence by a thrombin cleavage site. The expressed fusion protein iscleaved with thrombin to release SEQ ID NO:2.

The Epo-bp of SEQ1O ID NO:2 is found naturally in human serum andplasma, possibly produced as a cleavage product of Epo receptor (seeExample 2 below). In particular embodiments, the soluble Epo-bp has atleast 70%, at least 80%, or at least 90% amino acid sequence identity toSEQ ID NO:2, as calculated using the default BLAST parameters fornucleotide sequence comparison at the PubMed website,vvwvv.ncbi.nlm.nih.gov/PubMed/.

In some embodiments of the invention, the soluble Epo-bp is SEQ ID NO:8,which is SEQ ID NO:2 with the additional two residues Gly-Ser at theamino terminus. In one embodiment of the invention, the soluble Epo-bpis a product of a process comprising: expressing a fusion protein andcleaving it with thrombin. The fusion protein consists essentially of afirst polypeptide segment having a thrombin proteolytic cleavage site atits carboxyl terminus, and a second polypeptide segment consistingessentially of SEQ ID NO:2. The amino terminus of the second segment iscovalently coupled to the carboxyl terminus of the first segment. Thesoluble Epo-bp is produced by cleaving the fusion protein with thrombin.

In one embodiment of the invention, the soluble Epo-bp is a product of aprocess comprising: expressing a fusion protein comprising SEQ ID NO:2linked at its amino terminus to a peptide sequence ofLeu-Val-Pro-Arg-Gly-Ser (SEQ ID NO:7), and cleaving the fusion proteinwith thrombin.

In one embodiment of the invention, the soluble Epo-bp is a product of aprocess comprising: expressing a fusion protein consisting of: (a) afirst polypeptide segment having an amino terminus and a carboxylterminus, said segment having SEQ ID NO:7 at its carboxyl terminus; and(b) a second polypeptide segment consisting of SEQ ID NO:2, the secondpolypeptide segment covalently coupled to the carboxyl terminus of thefirst polypeptide segment; and cleaving the fusion protein withthrombin.

In other particular embodiments of the methods of the invention, theagent is a recognition protein that binds Epo receptor on anextracellular soluble portion of the Epo receptor. The recognitionprotein may exert its effect of reducing the Epo-induced blood pressureincrease by binding to the extracellular soluble portion of intact Eporeceptor molecules in membranes, or it may exert its effect by bindingto the soluble Epo-binding protein that exists naturally circulating inblood (which has the same amino acid sequence as the extracellularsoluble portion of the Epo receptor, and may be a proteolytic product ofthe receptor), or by both of these mechanisms or other unknownmechanisms. Describing this embodiment of the agent as “a recognitionprotein that binds Epo receptor on an extracellular soluble portion ofthe Epo receptor” is intended to describe a characteristic of therecognition protein, and not to necessarily describe the mechanism ofaction of the recognition protein.

In a particular embodiment, the recognition protein binds SEQ ID NO:2.That is, the recognition protein recognizes and binds to some sequencewithin SEQ ID NO:2. The recognition protein could, for instance, be anantibody raised against SEQ ID NO:2, an antibody raised against the Eporeceptor where the antibody binds to SEQ ID NO:2, or an antibody raisedagainst a peptide fragment of SEQ ID NO:2. In particular embodiments,the recognition protein is an antibody. In particular embodiments, theantibody is a complete antibody. In particular embodiments, the antibodyis an antibody fragment. For instance, the antibody fragment may be anFab, Fab′, or F(ab′)2, or Fv. In particular embodiments, the antibody isan antibody against SEQ ID NO:2.

In other particular embodiments, the recognition protein is anon-antibody protein or peptide. For instance, it can be a recognitionpeptide or protein selected by phage display. Methods for selection ofbinding peptides using phage display are disclosed in Sidhu SS, Lowman HB, Cunningham B C, and Wells J A: Phage display for selection of novelbinding peptides. Methods in Enzymology 2000; 328:333-363.

In a particular embodiment, the agent is a combination of a soluble Epobinding protein and a recognition protein that binds Epo receptor on anextracellular soluble portion of the receptor.

Epo and the agent may be administered separately or together.

In particular embodiments, the amount of the agent administered 1s atleast equimolar with the amount of Epo administered. In particularembodiments, the amount of the agent administered is about equimolarwith the amount of Epo administered. For instance, the moles of theagent administered may be between 75% and 125% of the mole of Epoadministered. In particular embodiments of the method of treatinganemia, the agent reduces an erythropoietin-induced blood pressure risein the mammal. That is, the blood pressure of the mammal rises less whenthe mammal receives Epo and the agent, than when the mammal receives Epoalone. Preferably, when Epo is administered to a mammal with anequimolar amount of the agent, blood pressure increases no more than 75%as much as it rises when Epo is administered alone to the mammal, morepreferably no more than 50% as much as it increases when Epo isadministered alone to the mammal. One embodiment of the invention is apharmaceutical composition containing a recognition protein that bindsEpo receptor on an extracellular soluble portion of the Epo receptor.Another pharmaceutical composition of the invention includeserythropoietin and an agent selected from a soluble Epo-binding protein,a recognition protein that binds Epo receptor on an extracellularsoluble portion of the Epo receptor, and a combination thereof.

Another pharmaceutical composition of the invention includes a solubleEpo-binding protein. Typically, the pharmaceutical compositions includea pharmaceutically acceptable diluent or carrier. In one embodiment ofthe pharmaceutical compositions containing the recognition protein, therecognition protein is an antibody against SEQ ID NO:2. In oneembodiment of the pharmaceutical compositions containing the solubleEpo-binding protein, the Epo-binding protein is SEQ ID NO:2.

Other particular embodiments of the agent, the soluble Epo-bindingprotein, and the recognition protein that binds Epo receptor on anextracellular soluble portion of the Epo receptor are as described forthe methods of the invention.

Raising Antibodies:

To generate antibodies, Epo receptor or Epo-bp can be administereddirectly to a mammal, or the proteins or peptide fragments thereof canbe coupled to a carrier protein. Suitable carrier proteins includekeyhole limpet hemocyanin, bovine serum albumin, and ovalbumin. Methodsof coupling to the carrier protein include single step glutaraldehydecoupling and other methods disclosed in Harlow, Ed et al., Antibodies: alaboratory manual, Cold Spring Harbor Laboratory (1988). The immunogenis used to immunize a vertebrate animal in order to induce thevertebrate to generate antibodies. Preferably the immunogen is injectedalong with an adjuvant such as Freund's adjuvant, to enhance the immuneresponse. Suitable vertebrates include rabbits, mice, rats, hamsters,goats, sheep, and chickens.

Hybridomas to synthesize monoclonal antibodies can be prepared bymethods known in the art. See, for instance, Wang, H., et al., AntibodyExpression and Engineering, Am. Chem. Soc., Washington, DC (1995).Polyclonal and monoclonal antibodies can be isolated by methods known inthe art. See, for instance, id. and Harlow et al.

Native antibodies are tetramers of two identical light (L) chains andtwo identical heavy (H) chains. The L and H chains each have variabledomains that are responsible for antigen recognition and binding. Thevariability in the variable domains is concentrated in thecomplementarity determining regions (CDRs). An antibody that iscontemplated for use in the present invention can be in any of a varietyof forms, including a whole immunoglobulin, an antibody fragment such asFv, Fab, and similar fragments, a single chain antibody that includesthe CDR, and like forms, all of which fall under the broad term“antibody” as used herein.

The term “antibody fragment” refers to an antigen-binding portion of afull-length antibody. Antibody fragments can be as small as about 4amino acids, about 10 amino acids, or about 30 amino acids or more. Sometypes of antibody fragments are the following:

1. Fab is the fragment that contains a monovalent antigen-bindingfragment of an antibody molecule. A Fab fragment can be produced bydigestion of whole antibody with the enzyme papain to yield an intactlight chain and a portion of one heavy chain. Two Fab fragments areobtained per whole antibody molecule.

2. Fab′ is the fragment of an antibody that can be obtained by treatingwhole antibody with pepsin, followed by reduction to yield an intactlight chain and a portion of the heavy chain. Two Fab′ fragments areobtained per whole antibody molecule. Fab′ fragments differ from Fabfragments by the addition of a few residues at the carboxyl terminus ofthe heavy chain CHI domain including one or more cysteines.

3. F(ab′)2 is the fragment that can be obtained by digestion of wholeantibody with pepsin, without reduction. F(ab′)2 is a dimer of two Fab′fragments held together by two disulfide bonds.

4. Fv is the mmlmum antibody fragment that contains a complete antigenrecognition and binding site. Fv consists of a dimer of one H and one Lchain variable domain in a tight, non-covalent association (VH -VLdimer). It is in this configuration that the three CDRs of each variabledomain interact to define an antigen-binding site. Collectively, the sixCDRs confer antigen binding specificity to the antibody. However, even asingle variable domain (or half of an Fv comprising only three CDRsspecific for an antigen) has the ability to bind antigen, although at alower affinity than the complete binding site.

5. A single chain antibody (SCA) is defined as a genetically engineeredmolecule containing the variable region of the light chain and thevariable region of the heavy chain linked by a suitable polypeptidelinker as a genetically fused single chain molecule. The preparation ofpolyclonal antibodies is well known to those skilled in the art. See,for example, Coligan et al., in Current Protocols in Immunology, section2.4.1 (1992). The preparation of monoclonal antibodies is likewiseconventional. See, for example, Harlow et al., page 726.

Methods of in vitro and in vivo manipulation of monoclonal antibodiesare well known to those skilled in the art. For example, the monoclonalantibodies to be used in accordance with the present invention may bemade by the hybridoma method first described by Kohler and Milstein,Nature 256:495 (1975), or may be made by recombinant methods, e.g., asdescribed in U.S. Pat. No. 4,816,567. The monoclonal antibodies for usewith the present invention may also be isolated from phage antibodylibraries using the techniques described in Clarkson et al., Nature352:624 (1991), as well as in Marks et al., J. Mot Biol. 222:581 (1991).Another method involves humanizing a monoclonal antibody by recombinantmeans to generate antibodies containing human specific and recognizablesequences. See, for review, Holmes et al., J Immunol. 158:2192 (1997)and Vaswani et al., Annals Allerg y, Asthma & Immunol. 81:1050 (1998).

The monoclonal antibodies herein specifically include “chimeric”antibodies in which a portion of the heavy and/or light chain isidentical with or homologous to corresponding sequences in antibodiesderived from a particular species or belonging to a particular antibodyclass or subclass, while the remainder of the chain(s) are identicalwith or homologous to corresponding sequences in antibodies derived fromanother species or belonging to another antibody class or subclass, aswell as fragments of such antibodies, so long as they exhibit thedesired biological activity (U.S. Pat. No. 4,816,567; Morrison et al.,Proc. Nat'l. Acad. Sci. 81:6851 (1984)).

Methods of making antibody fragments are also known in the art (see, forexample, Harlow and Lane, Antibodies: a Laboratory Manual, Cold SpringHarbor Laboratory, New York (1988)). Antibody fragments of the presentinvention can be prepared by proteolytic hydrolysis of the antibody orby expression in E. coli of DNA encoding the fragment. Antibodyfragments can be obtained by pepsin or papain digestion of wholeantibodies by conventional methods. For example, antibody fragments canbe produced by enzymatic cleavage of antibodies with pepsin to provide a5S fragment denoted F(ab′)2. This fragment can be further cleaved usinga thiol reducing agent, and optionally a blocking group for thesulfhydryl groups resulting from cleavage of disulfide linkages, toproduce 3.5 S Fab′ monovalent fragments. Alternatively, an enzymaticcleavage using pepsin produces two monovalent Fab fragments and an Pcfragment directly. These methods are described, for example, in U.S.Pat. Nos. 4,036,945, and 4,331,647, and references contained therein.Other methods of cleaving antibodies, such as separation of heavy chainsto form monovalent light-heavy chain fragments, further cleavage offragments, or other enzymatic, chemical, or genetic techniques may alsobe used, so long as the fragments bind to the antigen that is recognizedby the intact antibody. For example, Fv fragments comprise anassociation of VH and VL chains. This association may be noncovalent orthe variable chains can be linked by an intermolecular disulfide bond orcross-linked by chemicals such as glutaraldehyde. Preferably, the Fvfragments comprise VH and VL chains connected by a peptide linker. Thesesingle-chain antigen binding proteins (sFv) are prepared by constructinga structural gene comprising DNA sequences encoding the VH and VLdomains connected by an oligonucleotide. The structural gene is insertedinto an expression vector, which is subsequently introduced into a hostcell such as E. coli. The recombinant host cells synthesize a singlepolypeptide chain with a linker bridging the two V domains. Methods forproducing sFvs are described, for example, by Whitlow et al., Methods: aCompanion to Methods in Enzymology, 2:97 (1991); Bird et al, Science242:423 (1988); Ladner et al., U.S. Pat. No. 4,946,778; and Pack et al.,Bio/Technology 11:1271(1993).

Another form of an antibody fragment 1s a peptide containing a singlecomplementarity-determining region (CDR). CDR peptides (“minimalrecognition units”) are often involved in antigen recognition andbinding. CDR peptides can be obtained by cloning or constructing genesencoding the CDR of an antibody of interest. Such genes are prepared,for example, by using the polymerase chain reaction to synthesize thevariable region from RNA of antibody-producing cells. See, for example,Larrick et al., Methods: a Companion to Methods in Enzymology, 2:106(1991).

The invention contemplates human and humanized forms of non-human (e.g.murine) antibodies. Such humanized antibodies are chimericimmunoglobulins, immunoglobulin chains, or fragments thereof (such asFv, Fab, Fab′, F(ab′)2 or other antigen-binding subsequences ofantibodies) that contain minimal sequence derived from non-humanimmunoglobulin. For the most part, humanized antibodies are humanimmunoglobulins (recipient antibody) in which residues from a CDR of therecipient are replaced by residues from a CDR of a non-human species(donor antibody) such as mouse, rat, goat, sheep, or rabbit having thedesired specificity, affinity, and capacity.

In some instances, Fv framework residues of the human immunoglobulin arereplaced by corresponding non-human residues. Furthermore, humanizedantibodies may comprise residues that are found neither in the recipientantibody nor in the imported CDR or framework sequences. Thesemodifications are made to further refine and optimize antibodyperformance. In general, humanized antibodies will comprisesubstantially all of at least one, and typically two, variable domains,in which all or substantially all of the CDR regions correspond to thoseof a non-human immunoglobulin and all or substantially all of the FRregions are those of a human immunoglobulin consensus sequence. Thehumanized antibody optimally also will comprise at least a portion of animmunoglobulin constant region (Fe), typically that of a humanimmunoglobulin. For further details, see: Jones et al., Nature 321:522(1986); Reichmann et al., Nature 332:323 (1988); Presta, Curr. OpinionStruct. Biol. 2:593 (1992); Holmes et al., I Immunol. 158:2192 (1997);and Vaswani et al., Annals Allergy, Asthma & Immunol 81:105 (1998).

Antibodies of the invention can also be mutated to optimize theiraffinity, selectivity, binding strength or other desirable property. Onemethod of mutating antibodies involves affinity maturation using phagedisplay. Affinity maturation using phage display refers to a processdescribed in Lowman et al., Biochemistry 30: 10832 (1991); see alsoHawkins et al., 1 Mol Biol. 254:889 (1992).

The invention will now be illustrated by the following non-limitingexamples.

EXAMPLE 1

The Example describes the preparation of an Epo-bp thought to have SEQID NO:2, as is also described in U.S. Pat. No. 5,843,726, Constructionof EpoR recombinant vector. A recombinant plasmid expression vector,pJYL26, was constructed from a PCR product having the human Epo receptorextracellular soluble domain coding sequence and from the plasmid vectorpGEX-2T, which was purchased from Pharmacia. PCR amplification wascarried out using a frill-length human EpoR cDNA, SEQ ID NO:4, as atemplate. The 5′-sense primer was 5′- TTGGATCCGCGCCCCCGCCTAAC-3′ (SEQ IDNO:5). This primer has a BamHl linker sequence at the 5′ end followed bythe coding sequence for amino acids 25-29 of the full-length human EpoRprotein. The 3′-antisense primer was 5′-TGAATTCGGGGTCCAGGTCGCT-3′ (SEQID NO:6). This primer has an EcoR 1 linker followed by sequencecomplementary to the coding sequence for amino acids 250 through 246 offull-length EpoR. PCR was carried out as described in U.S. Pat. No.5,843,726.

The PCR product and pGEX-2T were digested with EcoR 1 and BamHl, thedigested DNAs were purified with gel electrophoresis. The ligation wasdone with a mixture containing 1:g/:1 each of the PCR product andpGEX-2T. The ligated product was verified to be −5.5 kb. The ligatedplasmid mixture was used to transform E. coli JM109. Colonies weregrown. DNA was extracted from each transformed colony, and analyzed.Plasmid from one colony was selected after examining both EcoR 1 andEcoR 1 plus BamHl digested DNA sizes in 1% agarose gels to confirm thepredicted sizes. The procedures were carried out as described in U.S.Pat. No. 5,843,726, Purification of EpoRex-th fusion protein.Transformed E. coli containing the recombinant vector pJYL26 was grownand induced with IPTG. Cell extract was passed through a GSH-agarosecolumn. The bound EpoRex-th was eluted with reduced glutathione. Thiswas performed as described in U.S. Pat. No. 5,843,726. Purification ofEpo-QP. EpoRex-th contains a thrombin-specific proteolytic cleavagerecognition sequence separating Epo-bp from glutathione-S-transferase.The amino acid sequence of the cleavage recognition sequence isLeu-Val-Pro-Arg-Gly-Ser (SEQ ID NO:7). The fusion protein was cleavedwith thrombin, and Epo-bp was purified by affinity binding to anEpo-agarose column. This was performed as described in U.S. Pat. No.5,843,726. The amino terminus of the Epo-bp produced by this procedure,and thus the thrombin cleavage site, was not experimentally determined.The thrombin cleavage is believed to produce Epo-bp of SEQ ID NO:2. But,thrombin may cleave at other sites, such as between the Arg and the Glyof the recognition sequence to produce a protein having the Gly-Serpeptide attached to the amino terminus of SEQ ID NO:2 (SEQ ID NO:8).

EXAMPLE 2

This Example describes experiments testing the effect of administeringEpobp, which is a soluble Epo-binding protein having the amino acidsequence of SEQ ID NO:2, and an Fab antibody against Epo-bp, either withor without Epo, to rats.

EXPERIMENTAL PROCEDURES

Materials: Glutathione (GSH)-agarose, pGEX-2T expression vector andSEPHADEX G-50 were purchased from Pharmacia (Mechanicsburg, Pa). PCRreagents were from Perkin-Elmer Cetus (Norwalk, Conn.) and AFFIGEL® wasfrom BioRad (Richmond, Calif.). Bacteriophage T4 DNA ligase, restrictionenzymes and isopropylthio-13-Dgalactoside (IPTG) were purchased from BRLGibco (Gaithersburg, Md.). GENECLEAN ||was from Bio 101, La Jolla,Calif.. Nitrocellulose was from Schleicher & Schuell Co. (Keene, N. H.).Chemiluminescence (ECL) reagents and 1251-Epo were from Amersham(Arlington Heights, Ill.) and unlabeled Epo was a gift of Chugai-Upjohn(Rosemont, Ill.). Thrombin, trypsin, phenylmethylsulfonylfluoride(PMSF), diisopropylfluorophosphate (DFP), TRITON X-100,2,7-Dichlorofluoresein, biotin-amidocaproyl hydroazide, alkalinephosphatase conjugate, disodium p-nitrophenyl phosphate, ando-phenylenediaminedihydrochloride (oPD) were from Sigma (St. Louis,Mo.). Biotinylated rabbit anti-sheep antibodies, Avidin-horse radishperoxidase, and IgG purification Kit were from Pierce Co. (Rockford,Ill.). Streptavidin peroxidase was purchased from Boehringer ManheimCorp (Indianapolis, Ind.), and microplates were from Coming Costa(Cambridge, Mass.). All 5 other chemicals were of reagent grade.

Epo-bp, Fab antibody against Epo-bp (aEpo-bp), and Fab antibody againstEpo (aEpo) were prepared in our laboratory. Epo-bp was prepared asdescribed in U.S. Pat. No. 5,843,726. Epo-bp had the amino acid sequenceof SEQ ID NO:2. A full-length human EpoR cDNA (SEQ ID NO:4) was from Dr.Bernard G. Forget, Yale University. Oligonucleotides were synthesized bythe microchemical facility of the Institute of Human Genetics,University of Minnesota, Minn. All other chemicals were of reagentgrade.

Animal Study:

15 Male Sprague-Dawley (SD) rats were housed at the University AnimalCare facility with Purina Chow and drinking water freely accessible. Weexamined any circadian stage-dependence of Epo effects on the bloodpressure, hematocrit, body weight and spleen weight of the rats kept inan alternating light-darkness cycle from 04:00 to 18:00 for light. Toseek an effective treatment time, 5-week-old rats were assigned tocontrol or treatment groups, each group consisting of 6 subgroups, eachof 5 rats, in 6 test times at 00, 04, 08, 12, 16 and 20 hours. The ratswere randomly distributed into groups such that the baseline inter-groupdifferences in body weight, blood pressure and hematocrit of Epo Rxversus saline and other Rx groups were not statistically significant.Blood pressure, hematocrit, and body weight were measured just beforeand immediately after the completion of a 4-week course of twice-weeklyEpo (50 U/kg BW) or physiological saline subcutaneous injections. Epo,Epo-bp, and aEpo-bp dosage was determined based on Epoetin study reports(4). The Epo dose was 50 units per kg body weight, and an Epo-bp andaEpo-bp were administered in an amount equimolar with Epo. Theerythropoietin (Epoetin) was from Amgen Company (Thousand Oaks, Calif.).Affinity purified Epo-bp and aEpo-bp were prepared in our laboratories.The antibodies were digested to Fab fragments, and the Fab antibodieswere purified.

For blood pressure measurement, the femoral artery was cannulated underpentobarbital (50 mg/kg) anesthesia. At the end of the study, spleenswere weighed and photographed. The weights of the brain, heart, aorta,and L- and R-kidneys were also obtained.

Ligand Binding Site in Progenitor Cells and Detection of Epo and EpoR:

We developed ocEpo-bp in sheep inoculated with Epo-bp every 3-4 week for3 months. After collecting serum, the antibodies were purified anddigested to generate Fab antibodies. The Fab were purified. Fab werefluorescein labeled according to the manufacturer's description. Thesematerials were used to detect Epo receptor in blood and/or tissuesamples. Negative control cells had no antibodies added and positivecontrol cells had Fab from IgG of preimmune serum. To test for antibodybinding sites (Epo receptor) bone marrow cells were washed in PBS anddispensed at 1-3×103 cells per well in round-bottomed tubes andcentrifuged into a pellet at 500 g for 2 minutes. Supernatant wasremoved and 100 [1,1 of fluorescein-conjugated Fab antibodies wereadded. After mixing well, the mixture was incubated on ice for 30 mM.The cells were washed three times by adding 400 mill of buffercontaining 1% PCS and 0.01% NaN3 in PBS and centrifuged at 500 g for 2minutes to remove supernatant. The cells were resuspended in a totalvolume of up to 50 1.tl of PBS and analyzed under an invertedfluorescence microscope. Enzyme immunoassay (EIA) was used to detect andmeasure the levels of Epo, Epo-bp, and antibodies against Epo, andEpo-bp in healthy untreated human subjects. EIA microplates were coatedwith 2 pg/well of anti-Epo to detect Epo and 21.1 g/well of anti-Epo-bpto detect Epo-bp. To detect circulating anti-Epo and anti-Epobpantibodies, wells were coated with 2001.11 of 1:10 diluted serum orplasma in PBS, pH 7.4. Plates were incubated at room temperature for 30minutes or at 4° C. overnight. After coating the plates with antibody orserum, wells were washed 3 times with 200 .tl/well PBST (0.05% TWEEN 20in PBS). Nonspecific binding sites were blocked with 200 p 1/well 1% BSAin PBST for 30 mM at room temperature. Wells were washed 3 times with200 .tl/well PBST. To detect bound antigen, peroxidase-streptavidinlabel was attached to Fab anti-Epo (for detecting Epo), Epo (fordetecting anti-Epo antibodies), Fab anti-Epo-bp (for detecting Epo-bp),and Epobp (for detecting anti-Epo-bp) in our laboratory. Two microgramsof the appropriate

5 peroxidase-streptavidin-labeled protein in 200 ill PBST was added perwell. The wells were washed 3 times with 200 piPBST. A solution (160 LIDof o-phenylenediaminedihydrochloride (OPD) in citrate buffer was addedto each well. (The solution contained 10 mg/ml in 24 mM citrate, 51 mMNa2HPO4, pH 6.0, with 0.4 ml of 3% 1-1202 added to 100 ml of solutionimmediately before use.) The reaction was stopped by adding 40 [Ll of 5MNaOH, and the absorbance was measured at 405 nm.

Statistics:

Data were analyzed by two-tailed Student's t test, the cosinor methodand the linear least square rhythmometry (21), allowing variation as afunction of the data. Data are expressed as mean±SEM. A p value of lessthan 0.05 was considered significant.

RESULTS

In Table 1, before treatment, the inter-group differences for bloodpressure, hematocrit, and body weight in all treatment groups were notstatistically significant. Overall, body weight was lowered by Epocompared to control (295 vs. 313 grams, p<0.01). The reference circadianblood pressure differences in Epo treatment versus control, Epo-bp, andaEpo-bp (Fab antibody against Epo-bp) treatment groups before treatmentwere not statistically significant (87±2.8 vs. 88.8±3.4, 88.7±2.5,84.3±2.3 mm Hg). After treatment, the circadian blood pressure wassignificantly increased in the Epo treated group. The group comparisonsbetween Epo treatment versus control, Epo-bp, and ocEpo-bp treatmentgroups were as follows: 136.2±2.3 vs. 116.2±1.7, 118.4±2.1 and 116.6±2.1mm Hg, respectively, each p<0.0001. When Epo-bp or aEpo-bp was givenalong with Epo, however, blood pressure was maintained at similar levelsto the saline control group: 118.3 ±1.7 in the Epo-bp +Epo group and121.0 ±2.0 mm Hg in the aEpo-bp +Epo treatment group, which weresignificantly lower than that of the Epo treat group (136.2 ±2.3), eachp <0.0001.

TABLE 1 Overall Effects upon Circadian Body Weight, Blood Pressure,Hematocrit and Other Organ Systems in Various Treatments. Group (Rx) ybefore Rx (all group n = 30) BW (g) BP (mm Hg) Hct (%) Control (Saline)vs. SO.I ± 1.7 88.8 ± 3.4 36.2 ± 0.7 Epo 80.2 ± 1.4 87.1 ± 2.8 37.0 ±0.6 Epo-bp 81.6 ± 1.5 88.7 ± 2.5 36.5 ± 0.7 aEpo-bp 81.2 ± 1.3 84.3 ±2.3 36.1 ± 0.4 Epo + Epo-bp 81.0 ± 1.0 84.3 ± 3.4 36.3 ± 0.6 Epo +a.Epo-bp 79.4 ± 1.5 88.9 ± 2.6 37.1 ± 0.4 y after Rx BW (g) BP (mm Hg)Hct (%) SW (g) Brain W (g) Control (Saline) vs. 312.8 ± 4.9 116.2 ± 1.742.7 ± 0.8 0.86 ± 0.03 1.82 ± 0.01 Epo  294.9 ± 4.2*    136.2 ± 2.3***   61.6 ± 1.3***   1.58 ± 0.07***  1.77 ± 0.02* Epo-bp 312.1 ± 3.9 118.4± 2.1 43.9 ± 0.6 0.89 ± 0.02 1.80 ± 0.02 aEpo-bp 305.0 ± 4.9 116.6 ± 2.144.1 ± 0.7 0.85 ± 0.02 I.SO ± 0.01 Epo + Epo-bp 303.4 ± 3.6 118.3 ± 1.7  58.0 ± 1.1***   1.62 ± 0.05***  1.77 ± 0.02* Epo + a.Epo-bp 298.4 ±4.4 121.0 ± 2.0   59.1 ± 1.1***   1.79 ± 0.07***  1.76 ± 0.01** Epo vs.294.9 ± 4.2 136.2 ± 2.3 61.6 ± 1.3 1.58 ± 0.07 1.77 ± 0.02 Epo-bp  312.1± 3.9*   118.4 ± 2.1***   43.9 ± 0.6***   0.89 ± 0.02*** 1.80 ± 0.02aEpo-bp 305.0 ± 4.9   116.6 ± 2.1***   44.1 ± 0.7***   0.85 ± 0.02***1.80 ± 0.01 Epo + Epobp 303.4 ± 3.6   118.3 ± 1.7***   58.0 ± 1.1, t1.62 ± 0.05 1.77 ± 0.02 Epo + a.Epo-bp 298.4 ± 4.4   121.0 ± 2.0*** 59.1± 1.1 1.79 ± 0.07 1.76 ± 0.01 y after Rx Heart W (g) Aorta W (g)R-Kidney W (g) L-Kidney W (g) Control (Saline) vs. 1.03 ± 0.02 0.046 ±0.002 1.107 ± 0.02 1.092 ± 0.02 Epo  0.93 ± 0.02** 0.046 ± 0.002 1.076 ±0.02 1.084 ± 0.03 Epo-bp 1.03 ± 0.02 0.046 ± 0.002 1.106 ± 0.02 1.083 ±0.03 aE-Epo-bp 1.04 ± 0.02 0.044 ± 0.002 1.112 ± 0.02 1.099 ± 0.02 Epo +Epo-bp  0.96 ± 0.02* 0.046 ± 0.002 1.098 ± 0.02 1.073 ± 0.02 Epo +aEpo-bp 0.99 ± 0.02 −0.046 ± 0.002  1.084 ± 0.02 1.044 ± 0.02 Epo vs.0.93 ± 0.02 Epo-bp  1.03 ± 0.02** o:E-Epo-bp  1.04 ± 0.02** Epo + Epo-bp0.96 ± 0.02 Epo + aEpo-bp  0.99 ± 0.02* Rx: treatment; n = number ofrats (30 rats in each group); y: 24-h average; a: Epo-bp = anti-Epo-bpantibody; *p < 0.01; **p < 0.001; ***p < 0.0001; tp < 0.05 g = gram; BW= body weight; BP = blood pressure; HCT = hematocrit; SW = spleenweight; W = weight; R = right; L = left

Epo treatment increased hematocrit markedly overall as compared to thesaline, Epobp or aEpo-bp groups (61.6 vs. 42.7, 43.9 and 44.1%,respectively) and at each of the 6 test times, all p <0.0001.Administering Epo-bp or aEpo-bp together with Epo had almost no effecton the Epo-induced hematocrit increase (61.6% hematocrit in Epo vs.58.0% in Epo +Epo-bp and 59.1% in Epo +aEpo-bp Rx). But, significantly,both Epo-bp and aEpo-bp almost eliminated the Epo-induced blood pressurerise (136.2 mm Hg in the Epo-treated group, vs. 116.2 in saline control,118.3 for Epo+Epo-bp, and 121.0 in Epo+aEpo-bp). Thus, both Epo-bp andaEpo-bp protected the rats from the blood pressure rise caused by Epotreatment.

Splenomegaly characterized each rat in the Epo-treated group (spleenweight overall 1.58 vs. 0.86 for saline, 0.89 for Epo-bp, and 0.85 gramsfor aEpo-bp, each p<0.0001). Administering Epo-bp or aEpo-bp togetherwith Epo did not affect the splenomegaly. Brain and heart weights weresignificantly lower in the Epo Rx group as compared to all other groups,although the aorta and kidney weights were similar in each group.

FIG. 1 shows circadian blood pressures in all group comparisons in bargraphs±standard errors (SEM). The Epo-treated group had a significantlyincreased blood pressure as compared to all other 5 groups, eachp<0.0001. FIG. 2 shows circadian fluctuations of blood pressure in MESOR(about 24-h mean), amplitude and acrophase (peak time) in each treatmentgroup. Epo treatment increased circadian blood pressure (MESOR)significantly as compared to all other groups (all p <0.0001), althoughall group amplitude comparisons were not significantly different. Aftertreatment, the peak time in the Epo-treated rats was shifted to thedaytime as compared to control, Epo-bp or ocEpo-bp treatment groups(19:40 vs. 04:08, 05:44, 05: 16, respectively). It is an obvious shiftchange from the night to the daytime peak with Epo treatment in thisnocturnal animal. When Epo-bp or ocEpo-bp was given together with Epo,the shift change still remained in the same daytime range as in theEpo-alone treatment group (14:48, 19:20, respectively), although theEpo-bp+Epo and aEpo-bp+Epo groups' blood pressure levels were similar tothe control group.

Table 2 summarizes the circadian variations of body weight, bloodpressure, hematocrit and spleen weight in the 6 subgroups after Epo,Epo-bp and aEpo-bp treatments. The body weight difference betweenEpo-treated rats and any other treatment group was not statisticallysignificant among the 6 test times. A significantly increased bloodpressure in the Epo treated group was detected at 12, 16, 20 and 00hours, but not at 4.0 or 8.0 hours as compared to control, Epo-bp andaEpo bp Rx groups. Epo treatment increased hematocrit markedly overalland at each of the 6 test times as compared to control, Epo-bp andaEpo-bp Rx groups, all p<0.0001. The spleen weights were significantlyhigher in the Epo-treated group rats than those of the control, Epo-bpand aEpo-bp groups at all time points, although the body weight waslower at each time comparison.

TABLE 2 Circadian Variations of Body Weight, Blood Pressure, Hematocritand Spleen Weight in Various Treatments Group (Rx) 0400 0800 1200 16002000 0000 BW (gram): Saline vs. 313 ± 12 305 ± 09 324 ± 18 308 ± 13 310± 10 317 ± 13 Epo 305 ± 13 294 ± 07 294 ± 05 290 ± 05 295 ± 14 291 ± 14Epo-bp 314 ± 11 310 ± 06 303 ± 04 312 ± 10 319 ± 11 319 ± 13 aEpo-bp 314± 10 297 ± 20 308 ± 13 299 ± 06 293 ± 05 320 ± 12 Epo + Epo-bp 297 ± 10300 ± 04 301 ± 09 308 ± 11 301 ± 11 313 ± 09 Epo + a.Epo-bp 296 ± 13 286± 06 279 ± 04* 304 ± 12 305 ± 05 320 ± 13 BP (mm Hg): Saline vs. 116 ±5.8 120 ± 4.6 117 ± 3.7 108 ± 1.0 119 ± 3.2 118 ± 4.1 Epo 131 ± 7.6 131± 4.8 139 ± 3.9″′ 128 ± 8.1 t 140 ± 6.3* 137 ± 6.2t Epo-bp 118 ± 4.5 122± 5.5 118 ± 3.6 115 ± 4.0 118 ± 6.1 120 ± 7.7 a.Epo-bp 113 ± 5.7 122 ±5.1 117 ± 4.7 112 ± 3.4 113 ± 4.6 122 ± 6.8 Epo + Epo-bp I14 ± 2.2 121 ±3.1 118 ± 6.9 121 ± 4.5t 119 ± 4.0 117 ± 3.8 .Epo + o:Epo-bp 116 ± 6.7121 ± 4.1 120 ± 6.2 120 ± 5.0t 127 ± 5.6 122 ± 1.4 Epo vs. 118 ± 4.5 122± 5.5 118 ± 3.6″′ 115 ± 4.0t 118 ± 6.1 t 120 ± 7.7 Epo-bp aEpo-bp 113 ±5.7 122 ± 5.1 117 ± 4.7* I12 ± 3.4t 113 ± 4.6* 122 ± 6.8 Epo + Epo-bp114 ± 2.2 121 ± 3.1 118 ± 6.9t 121 ± 4.5 119 ± 4.0t I17 ± 3.8t Epo +a.Epo-bp 116 ± 6.7 121 ± 4.1 120 ± 6.2t 120 ± 5.0 127 ± 5.6 122 ± 1.41Hct (%): Saline vs. 42 ± 2.6 41 ± 2.3 42 ± 1.6 44 ± 0.5 45 ± 1.4 43 ±3.0 Epo 60 ± 4.5* 64 ± 2.2*** 66 ± 2.7*** 65 ± 1.5*** 61 ± 3.8* 64 ±1.5** Epo-bp 45 ± 1.4 45 ± 1.6 44 ± 1.1 41 ± 2.2 45 ± 0.6 43 ± 1.9aEpo-bp 47 ± 1.0 45 ± 0.8 43 ± 0.8 43 ± 3.2 43 ± 2.2 44 ± 0.9 Epo +Epo-bp 58 ± 1.9** 62 ± 1.8*** 60 ± 2.9** 62 ± 2.5*** 54 ± 3.2t 53 ± 3.5Eoo + o.Eoo-bo 61 ± 2.0*** 64 ± 1.9*** 60 ± 2.7*** 57 ± 4.0t 57 ± 3.2*55 ± 1.8* SW (gram): Saline vs. 0.88 ± 0.1 0.82 ± 0.1 0.88 ± 0.1 0.96 ±0.I 0.73 ± 0.1 0.92 ± 0.1 Epo 1.65 ± 0.2* 1.70 ± 0.2** 1.69 ± 0.1^(•••)1.63 ± 0.1* 1.37 ± 0.1 * 1.23 ± 0.1 t Epo-bp 0.87 ± 0.0 0.87 ± 0.0 0.87± 0.0 0.94 ± 0.1 0.97 ± 0.1 t 0.83 ± 0.1 a.Epo-bp 0.82 ± 0.0 0.92 ± 0.10.87 ± 0.0 0.80 ± 0.1 0.79 ± 0.1 0.89 ± 0.0 Epo + Epo-bp 1.50 ± 0.1*″′1.58 ± 0.1 *** 1.67 ± 0.1*** 1.62 ± 0.2* 1.48 ± 0.1*** 1.86 ± 0.1 ***Epo + aEpo-bp 1.69 ± 0.1 *** 1.54 ± 0.2** 1.53 ± 0.I*** 1.80 ± 0.1*″′1.90 ± 0.2*** 2.27 ± 0.3** Epo vs. 0.87 ± 0.0** 0.87 ± 0.0** 0.87 ±0.0*** 0.94 ± 0.1 * 0.97 ± 0.1 0.83 ± 0.1 t Epo-bp aEpo-bp 0.82 ± 0.0**0.92 ± 0.1* 0.87 ± 0.0*** 0.80 ± 0.1** 0.79 ± 0.1* 0.89 ± 0.0* Epo +Epo-bp 1.50 ± 0.1 1.58 ± 0.1 1.67 ± 0.1 1.62 ± 0.2 1.48 ± 0.1 1.86 ±0.1* Epo + aEpo-bp 1.69 ± 0.1 1.54 ± 0.2 1.53 ± 0.1 1.80 ± 0.1 1.90 ±0.2 2.27 ± 0.3* Rx = Treatment; n = 5 rats in each subgroup; *p < 0.01;**p < 0.00I; ***p < 0.0001; tP < 0.05; BP = Blood pressure; BW = Bodyweight; Hct = Hematocrit; SW = Spleen weight.

FIG. 3 shows circadian hematocrit compansons. There was not only anincreased hematocrit but also the peak time of hematocrit shifted fromnight (20: 15) to a late morning hour (11:16) with Epo-treatment. In thegraph, groups of a (control), c (Epo-bp) and d (aEpo-bp) are located inthe dark cycle plane, while groups of b (Epo), e (Epo+Epo-bp), and f(Epo±aEpo-bp) are located in the light cycle plane. Again, it is anobvious shift change from the night to the daytime peak in Epo Rx inthis nocturnal animal. MESOR comparisons in cYo hematocrit in Epo (61.6)vs. control (42.7), Epo-bp (43.9) and aEpo-bp (44.1) treatment were allstatistically significant in each time point comparison (each p<0.0001).The amplitudes of the circadian peak-to-peak differences in hematocritwere not significantly different between the treatment groups. But theamplitudes were larger in the Epo-treated groups than in the groups thatdid not receive Epo (2.40 in Epo, 4.41 in Epo+Epo-bp, and 3.59 inEpo±aEpo-bp, versus 1.65 in control, 1.13 in Epo-bp and 1.73 inaEpo-bp).

In FIG. 4, splenomegaly (a, b and c) characterized each Epo treated ratwhen compared with the saline treated rats (FIG. 4, panel d). The spleenweight was significantly higher in Epo treated rats, as compared tothose of control, Epo-bp and aEpo-bp Rx groups (Tables 1 and 2). Theresults suggest that the time of the Epo treatment, with or withoutEpo-bp and/or aEpo-bp treatment may be important. Epo-bp and aEpo-bpprotect against the Epo-caused blood pressure rise, while not reducingthe Epo-increased hematocrit levels. Epo dose in clinical use should bereevaluated to prevent further systemic and local adverse effects, suchas high blood pressure and other organ damages. The binding sites ofblood cell progenitors were identified using Epo-bp and antibodiesagainst it. Fluorescein-labeled aEpo-bp was used to visualize receptorsites of bone marrow progenitor cells. No receptors were detected withfluorescein-labeled preimmune Fab, or in negative control cells. Butlabeled aEpo-bp did detect binding sites on megakaryocytes,erythroblasts, normoblasts, and myeloblasts (data not shown). [0082] Thelevels of Epo, Epo-bp, and antibodies against Epo and Epo-bp weremeasured in serum and plasma in healthy untreated humans by enzymeimmunoassay (EIA The EIA results are presented in FIG. 5. Opticaldensity (OD) of each measurement is presented as the mean±SEM of 8-14individual samples in duplicates. The OD values presented in FIG. 5 werecalculated by subtracting the OD value of the blanks from the OD of eachsample. Serum and plasma Epo and Epo-bp OD values were similar to eachother: 0.308±0.026 serum Epo, 0289±0.022 serum Epo-bp, 0.289±0.028plasma Epo, and 0.299±0.015 plasma Epo-bp. The plasma level ofanti-Epo-bp antibody was significantly lower than those of the otherthree antibody categories: 0.058±0.008 serum aEpo, 0.052±0.006 serumaEpo-bp, 0.054±0.013 plasma aEpo, and 0.031±0.004 plasma aEpo-bp. SerumaEpo and aEpo-bp levels were similar but the concentration of plasmaaEpo-bp was significantly lower than the concentration of serum aEpo,serum aEpo-bp, or plasma aEpo (p<0.025). The Epo and Epo-bp values wereconverted with known Epo concentrations prepared as controls in the sameplate to mU/ml. The converted values in mU/ml were 25.4±2.17 mU serumEpo, 24.2±2.35 mU plasma Epo; 24.2±1.84 mU serum Epo-bp, 25.0±1.26 mUplasma Epo-bp. This assay method is simple and more sensitive than theradioimmunoassay (17.7±6.3 mU/ml of Epo) and gives a much smaller SEM.Furthermore, the materials used in the preparation are moreenvironmentally friendly than radioactive or other toxic chemicals usedin conventional methods.

DISCUSSION

As expected, we observed an increase in blood pressure in theEpo-treated group. In addition, the hematocrit was markedly increasedoverall and at each of the 6 test times in the Epo-treated rats, andsplenomegaly characterized each rat with the Epo treatment. Epotreatment not only significantly increased blood pressure but alsoshifted the peak time of blood pressure from the night to the daytime.Remarkably, Epo-bp and aEpo-bp protected the rats almost completely fromthe Epo-induced rise in blood pressure, while not reducing hematocritpercent. The mechanism of this protective effect is not known. We couldspeculate, however, that Epoetin (recombinant Epo currently in clinicaluse) may induce some toxic materials in the living animal body whenrepetitively injected. Epo-bp and/or ocEpo-bp might bind and eliminatethe toxic materials, since Epo-bp binds Epo or its degradation products,and VEpo-bp might also bind certain products induced by Epo treatment.

FIGS. 2 and 3 show that Epo, as well as combination treatment withEpo+Epo-bp or Epo+VEpo-bp caused a shift in the circadian time of peakblood pressure. This suggests that treatment time for treatment withEpo, Epo +Epo-bp, or Epo +VEpo-bp may markedly affect the outcome. Anindividual's genetic susceptibility to endocrine treatment, as shown bysalt susceptibility to hypertension in Dahl rats, also must beconsidered (22,23).

The cloning of the human Epo-receptor recombinant vector JYL26 andpurification of the pure human Epo-bp and its antibodies were importantbenchmarks to allow us to visualize the ligand binding sites and toidentify the cell type where the Epo receptor is located (Lee, U.S. Pat.No. 5,843,726). To identify the ligand binding site, we developedseveral sensitive and simple methods. These may allow us to understandthe structure of the Epo receptor, and examine the factors involved inligand binding, as well as to identify other factors involved inregulating differentiation and proliferation of the progenitor cells. Inthis study, we report the direct binding of Epo to our purified humanEpo-bp. Our Epo-bp and its antibodies are to our knowledge the firstpurified pure human Epo receptor gene products, which are characterizedin specific binding of Epo and its antibodies in nM concentrations. Thebinding sites of blood progenitor cells were elaborated using Epo-bp andits antibodies. These data support the current proposal that all humanprogenitor blood cells contain Epo receptors and bind Epo. We do notknow what the biophysiological mechanisms of Epo or the second messengersystem involved in response to the Epo-Epo receptor interaction are. Themethods presented in this report will help identify defects related toEpo or Epo receptor, and elucidate the role of Epo receptor (EpoR) inprogenitor processes and ligand binding. The results may help inunderstanding the structural and functional relationship of Epo-EpoRinteractions in blood cell progenitors. The sensitive detection may helpus to understand the role of the Epo-EpoR interaction in blood cellproduction and diseases of blood cell production and help to developtreatment methods for hematological malignancies and some systemiccardiovascular diseases, such as high blood pressure.

CONCLUSIONS

Epo treatment increased hematocrit markedly overall as compared to thesaline control, Epo-bp, and anti-Epo-bp antibody (aEpo-bp) treatedgroups, and did so at each of the 6 test times, all p<0.0001. Increasedblood pressure was detected at 12, 16, 20 and 00 hours, but not at 04 or08 hours in rats treated with Epo. When Epo-bp or aEpo-bp was given inconjunction with Epo treatment, blood pressure was maintained at similarlevels to the control group. However, hematocrit levels were notsignificantly changed in Epo treatment vs. Epo+Epo-bp or Epo+aEpo-bptreatment groups (61.6 vs. 58.0 or 59.1%, respectively). Thus, Epo-bpand aEpo-bp reduce or prevent the Epo-induced rise in blood pressure.

Body weight was lowered by Epo treatment. Splenomegaly characterizedeach rat in Epo treatment. Brain and heart weights were significantlylower in the Epo treated group as compared to all other groups. Thesedata suggest that Epo dose should be reevaluated to prevent furtherorgan damage. The circadian results indicate that the time of the Epotreatment, alone or in combination of Epo-bp and/or aEpobp, may also beimportant.

Serum and plasma levels of Epo, Epo-bp, and antibodies against theproteins in untreated human volunteers were determined. Serum and plasmaEpo and Epo-bp levels were similar: Epo25.4±2.17; 24.2±2.35; and Epo-bp24.2±1.84; 25.0±1.26 mU/ml, respectively. Serum aEpo and aEpo-bp levelswere similar, but the plasma aEpo-bp level was significantly lower thanthat of serum or plasma aEpo or serum aEpo-bp.

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All of the patents, patent documents, and references cited herein arehereby incorporated by reference thereto.

1. A method of treating anemia in a patient, comprising: administering to the patient both erythropoietin (Epo) and an antibody that binds SEQ ID NO:2.
 2. The method of claim 1 wherein the antibody is an antibody fragment.
 3. The method of claim 2 wherein the antibody fragment is Fab.
 4. The method of claim 1 wherein the Epo and the antibody are administered together.
 5. The method of claim 1 wherein the Epo and the antibody are administered separately.
 6. The method of claim 1 wherein the amount of antibody administered is at least equimolar with the amount of the Epo administered. 